This invention concerns improvements in or relating to networked communication devices and systems employing such networked devices. The invention has particular, but not exclusive application to systems in which a plurality of networked communication devices such as transceivers are arranged to communicate wirelessly with a master controller to control operation of the devices and/or to provide information relating to the status of the devices. More especially, the invention relates to systems employing spread spectrum communication between networked communication devices and a master controller. The invention may be employed in aircraft to control operation of safety systems in an emergency such as emergency lighting systems to assist evacuation of the aircraft, for example in the event of an accident, or deployment of oxygen masks, for example following sudden de-pressurisation of the cabin. The invention may also be employed to provide information on the status of such systems and/or information relating to other systems relating to safety of the aircraft, for example smoke detection systems.
Conventional electrically powered lighting systems provided in aircraft for normal use are hard wired with electrical wiring connecting individual light sources to a remote power source, typically storage batteries. Such systems may be rendered inoperable following an accident if the electrical wiring connections to the power source are damaged. For example, the electrical wiring connections may be broken by impact damage to the structure of the aircraft, and/or by fire and/or by water if the aircraft has to make an emergency landing on land or in the sea.
For this reason, it is a mandatory requirement to fit aircraft with emergency lighting systems at ceiling and floor level that are operable independently of the normal lighting system to provide back-up in the event of failure of the latter and to assist evacuation of the aircraft.
Traditionally, these emergency lighting systems have also been electrically powered with hard wiring connecting the light sources to a remote power source such as storage batteries separate from the electrical lighting system for normal use. This adds considerably to the installation costs.
Furthermore, being electrically powered, these known emergency lighting systems have been susceptible to failure at the time they are required. For example, damage to the power source (e.g. storage batteries) and/or the electrical wiring connections may prevent operation of the emergency lighting system in exactly the same way that the overhead electrical lighting systems for normal use may be rendered inoperable.
Another disadvantage of electrically powered emergency lighting systems is the additional servicing and maintenance work that has to be carried out to keep the system in good condition. Thus, the power source, electrical wiring, connections and light source such as bulbs have to be checked regularly and any damaged or broken parts replaced.
We have previously proposed in European Patent No.0828657-B1 a floor mounted emergency lighting system employing photoluminescent material arranged in a track extending along one or both sides of the aisle. The photoluminescent material is operable to emit light automatically to identify an escape route at low levels of illumination, for example if the normal overhead lighting is inoperable following a crash.
More particularly, the photoluminescent material is activated by exposure to a light source such as ambient light or the normal overhead lighting and releases light by means of the stored energy from such activation. In this way, the photoluminescent material is self-illuminating to identify an escape route for guiding passengers to an emergency exit at the time it is needed without any connections to a separate power source such as storage batteries required by conventional electrically powered emergency lighting systems.
Furthermore, the emission of light by the photoluminescent material is unaffected by damage to the track(s) and the emergency lighting system continues to operate even if the aircraft breaks up into several parts. As a result, the track(s) identify an escape route which passengers can follow to an exit or to an opening in the body of the aircraft to escape in an emergency.
This system has been widely adopted with success by many aircraft operators. However, to comply with current regulations, electrically powered vertical exit identifiers (VEIs) have to be provided to identify the exits below 48″. These require hard wiring connections to a remote power source (storage batteries) and may therefore be inoperable if the wiring connections are damaged.
Similar problems exist with other safety systems typically provided in aircraft that rely on hard wiring connections to an electrical power source to operate in an emergency. For example, drop-down oxygen masks provided in the cabin to allow the passengers to breathe if the cabin suddenly de-pressurises are electrically operable and may be rendered inoperable if the cause of the de-pressurisation also damages the hard wiring connections.
Accordingly, the problems and disadvantages of electrically powered hard wired safety systems on aircraft remain.
The present invention has been made from a consideration of the aforementioned problems and disadvantages of existing hard wired electrical safety systems used in aircraft.
Thus, it is a desired aim of this invention to provide further improvements in safety systems employed on aircraft.